Conventional technologies of virtual sound localization include a method of localizing virtual sound in front of and behind a listener using an HRTF.
With this method, virtual sound is generated as follows.
Firstly, a speaker is placed at a desired position of virtual sound localization, and then an HRTF is measured from this speaker to the entrance of the external ear canal of the listener. This measured HRTF is set as a target characteristic. Following this, an HRTF is measured from a reproduction speaker to a listening position. Here, the reproduction speaker is used for reproducing a reproduction-target sound source. This measured HRTF is set as a reproduction characteristic. Note that the speaker placed at the desired position of virtual sound localization is used only for measuring the target characteristic and thus is not used for sound reproduction. Only the reproduction speaker is used for reproducing the reproduction-target sound source.
Then, an HRTF used in virtual sound localization is calculated from the target characteristic and the reproduction characteristic. The calculated HRTF is set as a filter characteristic. This filter characteristic is convoluted into the reproduction-target sound source which is then reproduced from the reproduction speaker. As a result, virtual sound localization can be implemented in such a manner that it seems to the listener as if the sound was reproduced from the speaker placed at the desired position of sound localization, although the sound is actually being reproduced from the reproduction speaker.
For generating the virtual sound as described above, there are two cases where: (1) reproduction speakers for reproducing the reproduction-target sound source are placed in front of the listener typically as in the case of a front virtual surround system; and (2) front speakers are placed in front of the listener and near-ear speakers are placed near the ears of the listener. A method for further increasing the accuracy in virtual sound localization by using the front speakers and the near-ear speakers is disclosed (see Patent Literature 1).